In regard to optical materials such as optical films and optical molded articles, it is important to impart optical functions such as ultraviolet absorption and refractive index adjustment, and various investigations have been conducted.
Resin members are deteriorated under the effect of ultraviolet ray and suffered quality degradation such as discoloration or lowering of mechanical strength, so that long-term use of resin members is inhibited. In order to prevent such quality degradation or to control the wavelength of transmitted light, it has been a general practice to incorporate an inorganic or organic ultraviolet absorber into a resin member.
Inorganic ultraviolet absorbers have excellent durability such as weather resistance or heat resistance; however, since the absorption wavelength is determined by the band gap of the compound, the degree of freedom of selection is low, and there are only few compounds that can absorb even up to the long-wavelength ultraviolet ray region near 400 nm (UV-A, 315 to 400 nm) in the near ultraviolet ray range. Meanwhile, those inorganic ultraviolet absorbers that can absorb long-wavelength ultraviolet ray have absorption of wavelength up to 450 to 500 nm (visible range), and therefore, they cause coloration. Members used in solar cells and the like, development of which has advanced in recent years, need to be exposed to sunlight for a long period of time in the outdoors, and deterioration of the properties of the members as a result of exposure to ultraviolet ray over a long period of time, cannot be avoided. Therefore, there is a demand for an ultraviolet absorber having excellent light resistance, which exhibits durability against yellowing of members, and also exhibits a shielding effect for up to the UV-A region.
In contrast, organic ultraviolet absorbers are such that since the degree of freedom of structural design for the absorbers is high, ultraviolet absorbers having various absorption wavelengths can be obtained by devising the structures of the absorbers. On the other hand, organic ultraviolet absorbers are such that when a resin composition including an ultraviolet absorber is heated and then is subjected to molding and processing, there is a possibility that the ultraviolet absorber may be thermally decomposed, and this decomposition of ultraviolet absorber may lead to decrease in the ultraviolet absorbency of the resin member, impairment of transparency in the case of a transparent resin member, and contamination of molding and processing apparatuses. Thus, there is a demand for an organic ultraviolet absorber having superior heat resistance. Regarding organic ultraviolet absorbers, benzotriazole-based, benzophenone-based, triazine-based, cyanoacrylate-based and salicylate-based ultraviolet absorbers are conventionally known (see, for example, Patent Literatures 1 to 4).
On the other hand, in optical films such as a reflective film, an antireflection film, and a hard coat film, it is required to adjust the refractive index in order to regulate the optical characteristics. Conventionally, refractive index adjusting agents have been added for the adjustment of the refractive index. Regarding the refractive index adjusting agents, inorganic oxide particles and the like are used to increase the refractive index.
Furthermore, it is preferable that transparent resin members containing ultraviolet absorbers including optical molded articles are transparent after molding or after a lapse of time in view of applications, and thus ultraviolet absorbers are needed from the viewpoint of preventing deterioration of optical characteristics caused by opacification or discoloration due to ultraviolet-induced degradation. Particularly for glasses lens or contact lenses, ultraviolet absorbers are needed from the viewpoint of protecting eyes from ultraviolet ray.
In glasses lens and the like, increase of the refractive index of the resin proceeds, and there are additives, such as an ultraviolet absorber, having refractive indices that are lower than that of the resin. In this case, as the refractive indices of the additives are lower, and the amounts of addition of the additives become larger, the overall refractive index of the resin is lowered. Therefore, there is a need for an ultraviolet absorber which has a higher refractive index and can be added in high concentrations.